NEW YORK (Reuters Health) - Jaundice and phototherapy each increase a newborn's risk for childhood asthma, a Swedish study has confirmed.

The researchers had already seen this association in a smaller sample, but their first study had focused only on children who were hospitalized for their asthma. For the current report, published online April 27th in Pediatric Allergy and Immunology, the authors enlarged their cohort dramatically using data from the Swedish Medical Birth Register and the Swedish Prescribed Drug Register. They identified 1,337,472 children born between 1990 and 2003, including 61,256 who received prescriptions for anti-asthmatic medications.

After controlling for confounders, neonatal phototherapy and/or icterus carried an odds ratio of 1.30 for development of asthma between the ages of 2 and 12. When icterus was present but not phototherapy, the odds ratio for asthma before age 12 was 1.26, according to the article. When both icterus and phototherapy were present, the odds ratio rose to 1.41 (p = 0.03).

But lead author Dr. Sara Aspberg, of Karolinska Institute Stockholm, and colleagues did not look solely at jaundice and phototherapy, however. When they examined maternal and delivery risk factors, they found associations for first pregnancy (OR 1.14), involuntary childlessness for more than 1 year (OR 1.18), smoking during pregnancy (OR 1.08), maternal diabetes mellitus of any kind (OR 1.19), preeclampsia (1.24), cesarean section (1.30), and instrumental vaginal delivery (1.09).

Other neonatal risk markers for asthma included delivery after gestation of less than 32 weeks (OR 2.18) or less than 37 weeks (OR 1.52), low birth weight (<2500 g, OR 1.52; < 1500 g, OR 2.23), and being small for gestational age (OR 1.22). Respiratory problems, mechanical ventilation, and sepsis and/or pneumonia were also associated with an increased risk.

The authors can't explain the apparent association between phototherapy and asthma, but they point out that neonatal phototherapy has also been linked with type 1 diabetes. Since "asthma has been described as an autoimmune disease" and type 1 diabetes "is a classical autoimmune disease" it's possible that the two share common pathogenetic features, they suggest.